Groundplane mounted log periodic antenna



Jan 30, 1968 J. F. RAMs/w ETAL N 3,366,964

GROUNDPLANE MOUNTED LOG PERIODIC ANTENNA Filed Oct. 20, 1964 United States Patent Oce 3,366,964 Patented Jan. 30, 1968 3,366,964 GROUNDPLANE MOUNTED LOG PERIODIC ANTENNA John F. Ramsay, Huntington Station, and Charles W. Schumacher, Northport, N.Y., assignors to the United States of America as represented by the Secretary of the Air Force Filed Oct. 20, 1964, Ser. No. 405,303 7 Claims. (Cl. 343-792.5)

ABSTRACT F THE DISCLOSURE A log periodic antenna mounted on a groundplane with at least one of the base lines being a coaxial line. The radiating elements are in contact with the inner conductor with clearance space in the outer conductor and are alternately spaced on the base lines.

This invention relates to log periodic antenna systems and more particularly to log periodic antennas employing binocular coaxial lines.

A binocular coaxial line consists of two parallel similar coaxial lines.. The two coaxial lines .may touch along the length of their outer conductors or they may be spaced a small distance. A binocular line may be fed in phase (push-push) or in antiphase (push-pull). The input characteristic impedance of a binocular coaxial line is equal to twice the characteristic impedance of one member line, the lines being effectively in series.

In the present invention a binocular coaxial line is fed in antiphase with the input signal applied between the two inner conductors. The two outer conductors are spaced slightly and lie on a groundplane to which they are additionally bonded by groundstraps.

The binocular coaxial line bonded to a groundplane is used to feed a log periodic monopole array by tapping alternate monopoles of the array to each of the coaxial inner conductors of the binocular line avoiding contact with the outer conductors. The terminal of the binocular line remote from the input may be opened-circuited, short-circuited or provided with a load. In log periodic array of this type there is little power at the termination.

The explanation of the workability of the binocular feed to a log periodic monopole array is based on its derivation from the known log periodic dipole array. Consider only one monopole of the array; it possesses an image with the monopole and the image radiating as a dipole. Consider an adjacent monopole; it radiates as a dipole fed in antiphase. This antiphase feeding is regular along the array. Such feeding is that usually associated :ith log periodic dipole arrays. Hence, this monopole array on an innite groundplane radiates the same patterns as those of a corresponding log periodic dipole array.

It is, therefore, an object to provide a log periodic antenna using binocular feed.

It is another object to provide a log periodic monopole antenna that operates as a log periodic dipole antenna.

These and other advantages, features and objects of the invention will become more apparent from the following description taken in connection with the illustrative embodiments in the accompanying drawings wherein:

FIGURE 1 shows a perspective view of an embodiment of the invention;

FIGURE 2 shows a front view in elevation taken at 2-2 of FIGURE 1;

FIGURE 3 shows a perspective view of another embodiment of the invention; and

FIGURE 4 is a front View in elevation taken at 4-4 of FIGURE 3.

The considerations attaching to the design of log periodic ldipole arrays automatically apply to log periodic monopole arrays. The log periodic antenna conventionally has the general shape of a triangle formed in this case by the longitudinal axis of the coaxial lines and the individual radiating elements. The angle thus formed at the vertex of the triangle is a. The radial distance from the vertex to any point on any given element has a constant ratio 1- to the radial distance from the vertex to the corresponding point to the next adjacent element. Values of a, T, etc. can be selected as required by the antenna specification. Proof of these insertions has been obtained by testing a log periodic monopole array as shown in FIGURE 1. Satisfactory H-planes radiation patterns were obtained over the 4/1 band from 8 to 32 mc. for which the antenna was constructed. As is wellknown, this bandwidth is capable of being extended over wide limits far beyond 4/1 simply by continued construction of the log periodic monopole array to contain both smaller and larger elements. A VSWR of approximately 2/1 was measured over the range of 8 to 32 mc. and is possible to be maintained over a much greater frequency range.

The construction of a groundplane, monopole elements, coaxial line, etc., is an engineering project of relative ease utilizing components of standard type and little cost. For wide band applications in the High Frequency Band and the Very High Frequency Band, this type of antenna system has advantages not obtainable with any other known type.

Referring to FIGURES 1 and 2, binocular coaxial line 11 consists of two coaxial lines 12 and 13 having inner conductors 35 and 36 and outer conductors 37 and 38 respectively. Lines 12 and 13, lie on groundplane 14, and are bonded by groundstraps 15 to 23. The input to the binocular line is at 24 while the terminals remote from the input is at 25. Log periodic monopole elements 26 to 29 are mounted in binocular line 11 by inserting elements 26 to 29 in clearance holes 30 to 33 avoiding contact with outer conductors 37 and 38. Elements 26 to 29 are spaced alternately along line 12 and 13.

The embodiment shown in FIGURES 3 and 4 also uses a groundplane as a mirror to achieve log periodic dipole performance with a monopole array. The coaxial line 40 and parallel solid rod 41 are separated by thin strip 44 made of dielectric material and are coupled to groundplane 14 by thin strip 45 also made of dielectric material. A single coaxial line 39 feeds coaxial line 40. Log periodic monopole elements 26 to 29 are soldered to outer conductor 47 of line 40 and to rod 41 and are positioned alternately on the coaxial line 40 and parallel rod 41. As shown in FIGURE 4 inner conductor 43 of coaxial line 40 is connected to rod 41 by wire 42.

A model of the embodiment shown in FIGURES 3 and 4 gave frequency independent patterns over a 4/1 frequency range and a VSWR less than 2.5/ 1. The bandwidth performance can clearly be extended by constructing a longer array.

In both embodiments the lower members of a log periodic dipole arrangement are missing, being replaced by images in the groundplane. Thus, by using the present invention the effect of a log periodic dipole array can be obtained by using a log periodic monopole array in conjunction with a groundplane and with a binocular feed.

What we claim is:

1. A log periodic antenna system comprising:

(a) a groundplane;

(b) a pair of parallel coaxial lines each having an inner conductor and an outer conductor, the coaxial lines being mounted on the groundplane with the lower portion of the outer conductor in electrical contact therewith and the upper portion of the outer conductor having clearance holes for exposing the inner conductor; the holes being spaced at predetermined intervals and positioned alternately in the pair of coaxial lines;

(c) and a plurality of monopole elements arranged in log periodic manner inserted in the holes and in electrical contact with the inner conductor while avoiding Contact with the outer conductor.

2. A log periodic antenna system comprising:

(a) a coaxial line having an inner conductor and an outer conductor;

(b) a longitudinal conducting member positioned parallel to the coaxial line;

(c) a rst insulating strip interposed between the coaxial line and the longitudinal conducting member;

(d) a second insulating strip positioned beneath the coaxial line and the longitudinal conducting member in surface contact therewith, and essentially perpendicular to the first insulating strip;

(e) a groundplane positioned beneath the second nsulating strip and in surface contact therewith; (f) a plurality of monopole elements arranged in log periodic manner in contact with the longitudinal conducting member and the outer conductor of the coaxial line and positioned alternately therebetween at predetermined intervals.

3. A log periodic antenna system according to claim 2 wherein the longitudinal conducting member is a solid rod.

4. A log periodic antenna according to claim 2 which further comprises:

(a) a coaxial input line mounted on the first coaxial line;

(b) and means for shorting the first coaxial line to the solid rod at the opposite end.

5. A log periodic antenna system according to claim 1 wherein the plurality of monopole elements form a plane with a general shape of a triangle having a vertex and are spaced such that the radial distance from the vertex to any point on any given element has constant ratio T to the radial distance from the vertex to the corresponding point on the next adjacent element.

6. A log periodic antenna system according to claim 5 which further comprises means for feeding the antenna system in antiphase.

7. A log periodic antenna system according to claim 2 wherein the plurality of monopole elements are further positioned to form a plane with the general shape of a triangle having a vertex with a radial distance from the vertex to any point on a given element having a constant ratio -r to the radial distance from the vertex to the corresponding point on the next adjacent element.

References Cited UNITED STATES PATENTS 3,113,316 12/1963 Berry 343-7922 3,127,6 l2 3/1964 Granger 343-792-2 3,286,268 11/1966 Barbano 343-7922 HERMAN KARL SAALBACH, Primary Examiner. P. L. GENSLER, Assistant Examiner. 

